Sadness, check.
Pankamena hairstyle instead of foof hair, check.
I guess the only things seemingly out of place are the wiggly lines at the top...

I do like the floaty, dreamy feel of this one, and Pinkie is recognizable even with the flat mane. It did take me a couple of seconds of squinting to realize that she's holding a pillow between her arms, though. I think the way her mane breaks up her upper arm and the way the rightmost lines of her arm align with those of the pillow kind of make the whole pillow-and-arm bit feel like it's somehow sticking out from or detached from the rest of Pinkie. If you choose to color this one, it would probably help a lot with this complaint, though, since it'd be clearer that her arm and the pillow are separate objects.

I like the effect of the oblique lighting source showing the texture of the paper. I feel that to make this work best, the lines of the drawing should have stronger contrast. As suggested, coloring, along with adding thicker lines around the outside of objects, could help. I’m classing this as a mid tier piece.